Synchronous contact device for electric contact converters



I 19, 1954 ROLF 2,666,820

SYNCHRONOUS CONTACT DEVICE FOR ELECTRIC CONTACT CONVERTERS Filed Dec. 3,1951 2 Sheets-Sheet l 2 s 150. 1 I K- V} Fig. 3

Fig.4 lNvENT' R'.

ERlCH ROLF ATTY Jan. 19, 1954 E. ROLF 2,666,820

SYNCHRONOUS CONTACT DEVICE FOR ELECTRIC CONTACT CONVERTERS Filed Dec. 5,1951 2 SheetsSheet 2 Fig.5

INVENTOR'. ERtCH Ron. F

Patented Jan. 19, 1954 SYNCHRONOUS CONTACT DEVICE FOR ELECTRIC CONTACTCONVERTERS Erich Rolf, Nurnberg,

Siemens Schuckertwerke Aktiengesellschaft,

Berlin-Siemcnsstadt, Erlangen,

German corporation Germany, assignor to Germany, a

Application December 3, 1951, Serial No. 259,607

My invention relates to synchronous contact devices for electric contactconverters and is described hereinafter with reference to the drawingsin which:

Figs. 1 and 4 show basic circuit diagrams applicable for the invention,while Fig. 2 exemplifies the contact elements of one of the pertainingcontact devices, and Fig. 3 is a coordinate diagram explanatory of thecontact operation;

Fig. shows another coordinate diagram and is explanatory of theoperation of a contact device according to the invention, an embodimentof such a device being illustrated in Fig. 6.

Contact converters energized from threephase power supply lines haveheretofore predominantly been given a three-phase bridge circuit scheme(Graetz connection) of the type schematically shown in Fig. 1. Each ofthe three secondaries A of a power supply transformer is connectedthrough two inversely-phased contact rectifier groups BI and B2 to therespective posi tive and negative buses of a direct-current outputcircuit comprising a smoothing reactor C in series with the load D. InFig. 1, as well as in Fig. 4, each of the mechanically operating contactdevices, opening and closing in synchronism with the phase current to beswitched, is represented by the symbol of a valve element to alsoindicate the direction of the current flowing through the contact deviceduring its closing intervals. With such a circuit scheme, the closinginterval of each contact device must amount to 120 (electrical degrees)plus an additional overlapping (commutation) interval of a few tensdegrees and, hence, totals about 150. Contact closing intervals of thismagnitude can readily be obtained at high accuracy with the aid of amechanical drive having eccentric-actuated tappets whosemovement-versus-time characteristic is sinusoidal.

A tappet-actuated contact device of this kind is illustrated in Fig. 2.The device has two stationary contact members I, 2 and a movable bridgecontact member 3 biased toward its-closed position by a spring 4 restingagainst a fixed abutment 5. The contact member 3 is moved upwardly inopposition to spring 5 by means of a vertically reciprocating pusherelement'or tappet 6. Part of the tappet stroke is idle, the contactmember 6 being lifted only when the top face of the tappet rises abovethe level of the upper faces of the stationary contact members l and 2.The stroke movement of tappet 5 is in accordance. with a sinusoidal timecharacteristic as shown in Fig. 3;

According to Fig. 3, the sinusoidal half-wave 6 Claims. (Cl. 200-)movement of the tappet has an amplitude e so that the total tappetstroke amounts to 2e. For obtaining the above-mentioned contact closinginterval of 150, the halfway level S of the tappet top face must be adistance of but higher than the level K of the stationary contact faces.It is apparent that the speed of the movable contact member at theopening and closing moments is still nearly equal to the maximum speedof the tappet.

Other circuit schemes such as the six-phase bridge connection accordingto Fig. 4 (Latour connection) which would offer essential advantages forcontact converters over the three-phase bridge connection according toFig. 1, require a contact closing interval of only plus an overlappinginterval, amounting to a total of about A closing interval of such ashort duration can no longer be satisfactorily obtained with asinusoidal tappet movement. It will be seen from Fig. 3 that forsecuring such a short closing interval a much larger level difference ofhen would have to be chosen. This would result in much slower closingand opening speeds for the same tappet structure and, hence, can nolonger secure a satisfactory accuracy'of the switching performance.Sufficient contact speeds can be reached if the tappet structure isincreased considerably. This, however, leads to excessively highmechanical stresses, particularly of the contact spring (4 in Fig; 2),because the distance of spring deflection e-l-hso-is then increased to amultiple. It has been proposed to obtain short contact closing intervalswithout detrimental enlargement of the tappet stroke'by driving thetappets from curved cam disks with steep cam flanks instead of from theabove-mentioned eccentric drives. Such cam disks, however, are subjectto considerable wear at the high operating speeds required for the converters.

It is an object ofmy invention to provide a contact device for contactconverters which, though driven by an eccentric of sinusoidal'movement,aiiords an increased contact speed at the opening and closing momentswhile avoiding a detrimental increase in deflective movements of thcontact springs. More particularly, it is an object of the invention toprovide reliablecontact devices capable of satisfactory operation incontact converters of extremely short closing in tervals for instance ofabout 60.

To attain these objects and in accordance with my inventionI interpose,between an eccentric drive of sinusoidal movement and the movablecontact to be driven therefrom, a transmission whose output motion has atime characteristic departing from the sinusoidal law. Thischaracteristic has a larger than sinusoidal rate of change at theopening and closing moments without appreciable increase in springdeflection. This can beachieved by the superposition of at leasttwosinusoidal movements of different .respective frequencies.

According to another feature of my invention, the sinusoidal motion ofthe driving eccentric, occurring corresponding to that of the current tobe interrupted, is combined with a superimposed sinusoidal motion ofdoubled frequency produced by another eccentric, the superposition beingsuch that during one half-wave of the base frequency the tappet strokeis increased, while during the other half-wave the stroke is decreased.The increase in stroke acts in the sense of an increase in contactspeed. The stroke reduction during the other halfwave acts towardlimiting the spring deflection.

Theforegoing will be further understood'from the diagram of .Fig. 5.This diagram shows the superposition of a sinusoidal motion (H) of thebasefrequency by :a likewise sinusoidal motion (ll) of twice the basefrequency. Theresultant motion of the driving elements for the movablecontact is denoted by curve R. If the switching speed of the movablecontact and the deflection of the .biasingspring are assumed to be-equalto the respectivemagnitudes occurring in the 120 scheme (Figs. 1 and 3),then the amplitude of movement of the driving elements operating at thebase frequency'amountsto 84.5% of the corresponding amplitude occurringunder the conditions represented 'in Fig. 3, and the amplitude of themovement atthe double frequency amounts to only 18.5%.

The embodiment exemplified .in Fig. 6 :incorporates the just-mentionedperformance features. In this embodimentboth .sinusoidal components ofthe contact driving motion are produced by eccentrics, the eccentricforthedoubled frequency having twice the revolving :speed of the eccentricfor the base frequency. The contact device according to Fig. Ghas twoinversely operating pusher elements designed as tappets landB foractuating the respective movable contacts 9, l located above the tappet.top faces. The transmission upon the tappets of the sinusoidal movementat the base frequency is effected by meansof a three-armed angular leverll driven by a link 12 from an eccentric M which may be mounted on theshaft of a syn chronous motor (not illustrated). In order :to have theangular lever II also transmit to the tanp tsa movement oftwice the basefrequency, the. lever is pivoted at [8 on .an oscillatory :arm 15. Arm Ihas a pivot at 23 and is drivenby a link I! to reciprocateabout pivot 23at twice the base frequency. Movement is imparted to link i! by aneccentric l8 revolving attwice the speed of the motor. For this purpose,the eccentric l8 may be coupled with the motor shaft through spur gearsl3, I9 of a 2:1 transmission ratio. For releasing the eccentric I8 ofthe pressure of contact springs 20, 2| an additional spring 22 may beprovided. This spring 22 is shown tooperate as an expansion springalthough a compression spring may be usedinstead.

If a regulation of the overlap (commutation) intervals of the contactclosing periods .is re quired, the pivot 23 may preferably :be designedas. eccentric. By turning the ,journal shaft at a base "frequency 4 ofthis eccentric the elevation of the pivot point is displaced in adirection parallel to the contact movements thus decreasing orincreasing the contact closing interval in accordance with any desiredrequirements.

It will be recognized that in Fig. 5 thesinusoidal curve ([2)corresponds to the :motion of the link 12 in Fig. 6, while thesinusoidal curve (ll) of twice the frequency corresponds to the motionof link ll. The resultant curve R corresponds to the movement of thetappet I or 8. It will be seen that during the first half wave thetappet stroke isenlarged to'the value eres.

Consequently, the contact speedat the closing and openingmoments isconsiderably larger than the contact speedcorresponding to thesinusoidal motion (I2) at the base frequency. During the second halfwave, however, the resultant tappet stroke is diminished by the amounte2 over that occurring with a motion at the base frequency. Forinstance, by suitably dimensioning the cocentrics l4 and I8, it canreadily beachievedrthat the resultant distance F of spring deflection.according to Fig. 5 is not larger for .a 60 scheme than the springdeflection e+h12o according to Fig. 3 fora scheme. It should beremembered'that the diagrams of ,Figs.3 and :5 indi. cate the totalcontact interval (about :and 90 respectively) including the overlap(commutation) interval.

It will be obvious to thoseskilled :in the art upon a study of thisdisclosure thatmyinvention is not limited to the specific embodimentillustrated in Fig. 6 but may also be applied to other mechanisms forthe transmission and superposition of movements which modify thesinusoidal motion of .a driving eccentric :intoaia non-sinusoidal output:motion in the sense -:of an increased contact speed at the opening andclosing moments and a decreased deflection of the contact springs. I

I :claim:

1. Contact apparatus for electric contact converters, comprisingstationary contact meansya contact member reciprocable between closingand opening positions relative to said stationary contact means, springmeans engaging said member for biasingit to said closed'position, apusher element reciprocable tow-ardand awayfrom said contactmember andbeing inen'gagement :therewithalong a portion of the reciprocatingtravel of said element to move said member between said'positions, tworevolvable eccentrics of sinusoidal movement and respectively differentspeeds of revolution, and mechanism means Joined with said twoeccentrics for superimposing their respective movements and rbeing:joined withzsaid pusher element to impart resultant movement thereto.

2. Contact apparatus for electric contact "converters, comprisingstationary-contact means, a contact member reciprocable between closingand opening positions relative'to said stationary contact means, springmeans engaging said member for biasing it to said closed-position, arevolvable eccentric of sinusoidal movement, a transmission mechanisminputwise in engagement with said eccentric and having an output elementreciprocable toward and away from saidscontact member and being inengagement therewith alon a portion of the reciprocating travelof saidelement to move said member betweensaid positions, and drive means ofsinusoidal movement and. twice the frequency .cf said eccentric,,..saiddrive means being joined with said mechanism to superimpose said twosinusoidal movements upon said output element so that the travel of saidelement is longer than sinusoidal during one half revolution of saideccentric and shorter than sinusoidal during the other half revolution.

3. Contact apparatus for electric contact converters, comprisingstationary contact means, a contact member reciprocable between closingand opening positions relative to said stationary contact means, springmeans engaging said memher for biasing it to said closed position, apusher element reciprocable toward and away from said contact member andbeing in engagement therewith along a portion of the reciprocatingtravel of said element to move said member between said positions, aswing arm having a normally stationary pivot, an intermediate partfulcrumed on said arm at a point spaced from said pivot and engagingsaid pusher element to impart movement thereto, a first drive ofsinusoidal motion linked to said part to oscillate it at a basefrequency of a given value, and a second drive of sinusoidal motionlinked to said arm and having a frequency or twice aid value.

4. In contact apparatus according to claim 3, said two sinusoidal-motiondrives having respective eccentrics, and a gear transmissioninterconnecting said eccentrics at a fixed mutual phase relation atwhich the travel of said pusher element is longer than sinusoidal duringone half Wave of said base frequency and shorter than sinusoidal duringthe other half wave.

5. Contact apparatus for electric contact converters, comprisingstationary contact means, a contact member reciprocable between closingand opening positions relative to said stationary con tact means, springmeans engagin said member for biasing it to said closed position, atappet re ciprocable toward and away from said contact member and beingin engagement therewith along a portion of the reciprocating travel ofsaid element to move said member between said positions, a swing armhaving a normally stationary pivot,

an intermediate part fulcrumed on said arm at a point spaced from saidpivot and engaging said tappet to impart movement thereto, firsteccentric drive means of sinusoidal motion having a link pivoted to saidpart to oscillate it about said fulcrum at a frequency of a base value,second eccentric drive means of sinusoidal motion having a frequency oftwice said value, said second drive means having a link pivoted to saidarm at a point spaced farther from said pivot than said fulcrum pointfor oscillating said arm to superimpose said latter frequency upon saidtappet, and transmission means interconnecting said two eccentric drivemeans in a fixed phase relation to each other.

6. Contact apparatus for electric contact converters, comprisingstationary contact means, a contact member reciprocable between closingand opening positions relative to said stationary contact means, springmeans engaging said member for biasing it to said closed position, a,revolvable eccentric of sinusoidal movement, an oscillatory arm having afixed fulcrum axis and being linked to said eccentric to be oscillatedthereby, an oscillatory structure pivoted on said arm at a point spacedfrom said axis, oscillatory drive means linked with said structure andhaving a higher speed than said arm, said structure being engageablewith said contact along only a portion of the reciprocating travel ofsaid structure to move said member between said positions, saidstructure having a movement of a higher than sinusoidal rate of changeat the opening and closing moments of said member and having a shorterthan sinusoidal travel during engagement with said member.

ERICI-I ROLF.

References Cited in the file of this patent FOREIGN PATENTS Number

